1. Field of the Invention
The present invention relates to a method of supervising the function of a milking machine having a teatcup with a teatcup liner and a pulsation chamber, comprising applying a milking vacuum to the interior of the teatcup liner and a pulsating vacuum to the pulsation chamber so that the teatcup liner cyclically moves between a substantially open position and a substantially closed position. Moreover the present invention relates to a milking machine comprising a teatcup with a teatcup liner and a pulsation chamber, a vacuum source for generating a milking vacuum in the interior of the teatcup liner and a pulsator provided to alternately connect the pulsation chamber to the atmosphere and to said vacuum source for generating a pulsating vacuum in the pulsation chamber to produce a pulsating movement of the teatcup liner between a substantially open position and a substantially closed position
2. Description of the Prior Art
Traditionally a milking machine comprises a cluster having a claw and four teatcups, each teatcup having a shell and a teatcup liner provided in the shell to form a pulsation chamber between the teatcup liner and the shell. During milking the interior of the teatcup liner is subjected to a milking vacuum, that is a low pressure of normally about 50 kPa under atmospheric pressure. There are also milking machines working under high pressure conditions, whereby the low pressure might be above atmospheric pressure. The pulsation chamber is subjected to a cyclically pulsating vacuum normally varying between atmospheric pressure, when the teatcup liner is collapsed or closed, and maximum vacuum level when the teatcup liner is fully open. The maximum pulsating vacuum level is normally a low pressure level of 50 kPa under atmospheric pressure, i.e. equal to the milking vacuum level. This means that the pressure difference across the wall of the teatcup liner is essentially equal to zero when the teatcup liner is fully open.
The pulsating vacuum demonstrates a pulsation cycle which may be divided into four phases, i.e. (a) an opening phase during which the pulsating vacuum increases from atmospheric pressure to normally about the milking vacuum level and the teatcup liner moves from a closed position to an open position, (b) an open phase during which the pulsating vacuum has reached its maximum level and is essentially equal to the milking vacuum level and the teatcup liner is in an open position, (c) a closing phase during which the pulsating vacuum decreases from about the milking vacuum level to the atmospheric pressure and the teatcup liner moves from the open position to the closed position, and finally (d) a closed phase during which the pulsating vacuum is equal to the atmospheric pressure and the teatcup liner is in a closed position. The opening and closing of the teatcup liner during phase (a) and (c), respectively, comprises a very fast and abrupt movement of the teatcup liner. From a closed position, i.e. opposite wall portions of the teatcup liner touch each other, as the pulsating vacuum increases the teatcup liner remains essentially closed until it at a certain pulsating vacuum level, the so called TPD (touch pressure difference), starts to open abruptly to the so called CCPD (critical collapse pressure difference), at which pulsating vacuum level the teatcup liner is fully open, i.e. said opposite wall portions of the teatcup liner are spaced apart from each other. From the point of time when the pulsating vacuum exceeds the TPD-level the teatcup liner thus is essentially open and a further increase of the pulsating vacuum only results in an insignificant further opening of the teatcup liner. This very abrupt opening and closing is an important feature of the teatcup liner which ensure an effective massaging of the teat during milking.
However when the teatcup liners get older they soften and their elasticity or resiliency gradually diminish resulting in a less gentle teat treatment and less effective massaging of the teat. In the end this means that the productivity of the milking process decreases and that the teatcup liner has to be replaced by a new one.
Up to now the point of time for such a replacement has been chosen in accordance with a more or less fixed predetermined scheme, or by a manual check performed by the operator of the milking machine.
However, individual teatcup liners age differently, which means that one teatcup liner might require replacement after a relatively short period of time, or a relatively low number of milkings, while another one might function satisfactorily for a significantly longer period of time. In view thereof, a fixed scheme for replacement is of course not an optimal instrument, because it means that on one hand still well functioning teatcup liners might be replaced and that on the other hand milking might be performed by means of more or less worn-out teatcup liners. Moreover a manual check of the teatcup liners is time-consuming and not very reliable.
WO-A-9 314 625 discloses a milking apparatus including, for each claw a pulsator and a control unit responsive to the opening and closing of the teatcup liners. The pulsation switching characteristics of the pulsator are controlled by the control unit in sympathy with the opening and closing of the teatup liners in order to improve the pulsation effectiveness, i.e. to ensure a fully collapsing and opening of the teatcup liners in a single pulsation cycle. When the teatcup liners are fully closed or open the airflow in the pulsating vacuum pipe ceases. This cessation of air flow is detected by different means proposed in WO-A-9 314 625. For example such means comprises a piston and a cylinder device provided in the pulsating vacuum pipe, whereby the piston moves with the air flow and comes to rest at two opposite positions at which positions the piston is detected to give a signal to the pulsator to change between atmospheric pressure and low pressure. Other proposed means are a device comprising a rubber diaphragm moving in response to the air flow, a rotating turbine device, and a hot wire galvanometer.